Pump Driving Apparatus

ABSTRACT

A pump driving apparatus that can suppress backflow of a liquid in a pump chamber and improve pump efficiency is provided. 
     A guide tube  23  is provided coaxially with an output shaft  4  of a motor M inside a pump chamber  8,  and the ends in the axial direction of the guide tube  23  are fitted into and make sliding contact with a case inner wall surface that forms the pump chamber  8  and a shaft core-side inner wall surface  25  of an impeller  9  enclosed inside the pump chamber  8.

TECHNICAL FIELD

The present invention relates to a pump driving apparatus that drawsliquid in an axial direction into a pump chamber and expels the liquidin a circumferential direction by rotating an impeller provided insidethe pump chamber.

BACKGROUND ART

First, one example of a pump driving apparatus will now be described. InFIG. 6, a rotor magnet 53, which has been magnetized with two poles at180° intervals, is provided on a back yoke 52 of a rotor 51. The backyoke 52 is connected to a magnet case 56. A coupling magnet 55 is fittedonto the upper surface of the magnet case 56. The magnet case 56 isrotatably fitted onto a motor-side fixed shaft 54 a via a bearing 57. Apump-side fixed shaft 54 b, which is connected to a motor-side fixedshaft 54 a by screw engagement, is integrally provided on a pump chamber58. A rotation vane (impeller) 59 is fitted onto the pump-side fixedshaft 54 b via a bearing 60. The impeller 59 slidably rotates via thebearing 60 around the pump-side fixed shaft 54 b. A coupling magnet 61is provided on the impeller 59 so as to face the magnet 55. The magnets55, 61 are magnetized with six poles, for example, and the rotor 51 andthe impeller 59 rotate together due to magnetic coupling.

The pump chamber 58 is formed by screwing together a pump case 62 and amotor case 63 with a divider plate 64 in between. The pump chamber 58 issealed by an O ring 67 provided between the pump case 62 and the dividerplate 64. When the motor is driven, the impeller 59 that is magneticallycoupled to the rotor 51 rotates and thereby draws liquid from an inlet65 in the axial direction (i.e., the direction of the arrow P) into thepump chamber 58 and expels the liquid from an outlet 66 provided at theouter periphery of the pump case 62 in FIG. 7. In FIG. 8, protrudingribs 67 are formed on the impeller 59 so as to radiate outward from theinner periphery to the outer periphery. Due to centrifugal force causedby rotation of the impeller 59, the liquid is guided along theprotruding ribs 67 from the shaft core in FIG. 6 toward the outerperiphery in the direction of the arrow Q (see Non-Patent Document 1).

Non-Patent Document 1

Journal of Technical Disclosure 10,194,725

DISCLOSURE OF THE INVENTION

In the pump driving apparatus shown in FIG. 6, to ensure smooth rotationof the impeller 59 inside the pump chamber 58, a gap S is formed betweenthe impeller 59 and the inner wall surface of the pump case 62. This gapS is provided for the reasons given below. Firstly, it is necessary toprevent interference due to insufficient precision in the dimensions ofthe pump case 62 that is integrally molded. In addition, centering isdifficult for the impeller 59 which is formed by welding together anupper portion, where the radial protruding ribs 67 are formed, and alower portion, where the coupling magnet 61 is enclosed, which meansthat it is difficult to manufacture a pump driving apparatus withcomponents that are precisely concentric. Also, although it would beconceivably possible to increase the thickness of the divider plate 64to prevent eccentricity of the impeller 59 due to inclination of thefixed shafts 54 a, 54 b, this would cause a drop in the magneticattraction between the impeller 59 and the rotor 51 that aremagnetically coupled.

Most of the liquid that is drawn in near the shaft of the pump chamber58 from the inlet 65 is driven in the direction of the arrow Q towardthe outer periphery of the pump chamber 58 and expelled from the outlet66. However, a pressure difference is produced inside the pump chamber58, resulting in the problem that high-pressure liquid in the outerperiphery flows back, via the gap S between the impeller 59 and the pumpcase 62, in the direction of the arrow R toward the periphery of theshaft that is at low pressure and collides with the liquid being drawnin the direction of the arrow P. thereby lowering the pump efficiency.When the fixed shafts 54 a, 54 b are inclined, there is a furtherproblem in that the gap S will vary, resulting in greater fluctuationsin pressure inside the pump chamber 58, which makes the pump operationunstable.

It is an object of the present invention to provide a pump drivingapparatus that can suppress backflow of a liquid in a pump chamber andimprove pump efficiency.

To achieve the stated object, the present invention has the followingconstruction.

A pump driving apparatus draws in a liquid in an axial direction into apump chamber and expels the liquid in the circumferential directionusing an impeller that is magnetically coupled to a rotor of a motor androtates about a fixed shaft, the pump driving apparatus including aguide tube that is provided inside the pump chamber so as to be coaxialwith the fixed shaft, wherein ends of the guide tube in the axialdirection are fitted to and make sliding contact with a case wallsurface that forms the pump chamber and a core-side wall surface of theimpeller enclosed inside the pump chamber.

Several representative examples of sliding contact between the guidetube and the case wall surface and the core-side wall surface of theimpeller are given below.

Surfaces of the guide tube that make sliding contact may be sphericalsurface portions which are produced by having an outer circumferentialsurface of the guide tube swell outward and whose respective centers lieon an axis of the fixed shaft, and both ends of the guide tube in theaxial direction may be fitted into and make sliding contact with thepump case and an uprising wall surface of the impeller.

Alternatively, surfaces of the pump case and the impeller that makesliding contact may be spherical surface portions that are each producedby having an outer circumferential surface of an erected wall, which iserected in the axial direction inside the pump chamber, swell outwardand whose centers lie on an axis of the fixed shaft, and may be fittedinto a tube hole of the guide tube so as to make the sliding contact.

As another alternative, at one end in the axial direction, a sphericalsurface portion that is produced by having an outer circumferentialsurface of an erected wall, which is erected in the axial directioninside the pump chamber, swell outward and whose center lies on an axisof the fixed shaft may be formed on one of the pump case and theimpeller and the spherical surface portion may be fitted into a tubehole of the guide tube so as to make sliding contact, and at another endin the axial direction, a spherical surface portion that is produced byhaving an outer circumferential surface of the guide tube swell outwardand whose center lies on the axis of the fixed shaft may be formed onthe guide tube and the spherical surface portion may be fitted into anerected wall on one of the pump case and the impeller.

EFFECT OF THE INVENTION

When the pump driving apparatus according to the present invention isused, a guide tube is provided inside the pump chamber so as to becoaxial with the fixed shaft, wherein ends of the guide tube in theaxial direction are fitted to and make sliding contact with a case wallsurface that forms the pump chamber and a core-side wall surface of theimpeller enclosed inside the pump chamber. This means that when theimpeller is rotated to draw in low-pressure liquid in the axialdirection into the pump chamber and expel the liquid toward the outerperiphery, high-pressure liquid that flows back toward the core from theouter periphery of the pump chamber via a gap between the impeller andthe pump case due to the pressure difference in the pump chamber can beeffectively blocked by the guide tube. Therefore, it is possible toprevent vigorous collisions between high-pressure liquid that has flowedback in the pump chamber and the low-pressure liquid drawn in at thecore due to the pressure difference inside the pump chamber, andtherefore pump efficiency can be improved. Also, since it is possible toreduce the gap between the impeller and the pump case, it is possible toreduce redundant capacity of the pump chamber and make the pump chambermore compact.

Also, since each sliding contact surface formed on the guide tube or onan erected wall, which is erected in the axial direction inside the pumpchamber, of the pump case or the impeller is formed for example of aspherical surface portion that is produced by having an outercircumferential surface of the guide tube or the erected wall swelloutward and whose center lies on an axis of the fixed shaft, the guidetube will become inclined in keeping with any inclination of theimpeller due to fluctuations in pressure inside the pump chamber or thestrength of the fixed shaft. This means that the sliding contact betweenthe guide tube and the case wall surface and wall surface of theimpeller is maintained. As a result, it is possible to prevent vigorouscollisions between high-pressure liquid that flows back from the outerperiphery and the low-pressure liquid drawn in at the core due to thepressure difference inside the pump chamber, so that stable pumpoperation with little fluctuation in pressure inside the pump chambercan be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a principal part of a pumpdriving apparatus.

FIG. 2 is a perspective view showing a state where a magnet case and aback yoke are assembled.

FIG. 3A is an exploded perspective view showing the assembledconstruction of a pump driving apparatus and FIG. 3B is a partiallyenlarged view of a guide tube.

FIG. 4 is a schematic diagram showing sliding contact of the guide tube.

FIG. 5A to FIG. 5C are schematic cross-sectional views showing slidingcontact between the guide tube and a pump case and an impeller accordingto other examples.

FIG. 6 is a cross-sectional view of a conventional pump drivingapparatus.

FIG. 7 is a top view of the conventional pump driving apparatus.

FIG. 8 is a perspective view of a conventional impeller.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be described indetail with reference to the attached drawings. First, the overallconstruction of a pump driving apparatus will be described withreference to FIG. 1 to FIG. 3.

In FIG. 1, an example is shown where an outer-rotor, single-phase,bipolar brushless motor M is used as one example of a drive source fordriving a pump. In this single-phase, bipolar brushless motor M, a rotormagnet (not shown) that is magnetized with two poles at 180° intervalsis provided on a back yoke 2 of a rotor 1. The back yoke 2 is connectedto a magnet case 6. A coupling magnet 5 is fitted into an upper surfaceof the magnet case 6. The magnet case 6 is rotatably fitted via abearing 7 onto a motor-side fixed shaft 4 a. Note that the rotor 1 isenergized in the axial direction toward the magnet case 6 by aprecompressed spring provided at a fixed end of the stator.

Here, the single-phase, bipolar brushless motor M is driven as a DCbrushless motor by subjecting an AC current from a single-phase AC powersupply to full-wave rectification by a rectifying bridge circuit andhaving a control unit change the direction of the rectified currentflowing in the coil in accordance with the rotational angle of the rotor1 (i.e., the positions of the poles of the magnet). After this, once therotational speed of the rotor 1 approaches a rotational speed that issynchronized with the power supply frequency, there is a switch tosynchronous operation so that there is a transition to synchronousoperation. Note that the drive source is not limited to the single-phasebipolar brushless motor M, and it is also possible to use various typesof motor, such as a DC motor (as examples, a multipolar brushless motor,such as a single-phase four-pole brushless motor M, or a brush motor),an AC motor, or an induction motor. The motor is also not limited to anouter-rotor motor and may be an inner-rotor motor.

In FIG. 2, engagement holes 15 are formed around a protruding part,which protrudes downward in the axial direction, of a boss portion 14 ofthe magnet case 6 in which the bearing 7 is fitted. Engagementprotrusions 17 are also provided in the circumferential direction so asto protrude into a base portion through-hole 16 of the back yoke 2 thatis cup-shaped. Grease is applied to contacting parts of the magnet case6 and the back yoke 2 to reduce the frictional torque, and the magnetcase 6 and the back yoke 2 engage one another with a certain angle ofplay for relative rotation therebetween.

Next, the construction of the pump chamber 8 side will be described. Thepump chamber 8 is provided with a pump-side fixed shaft 4 b that isintegrally connected to the motor-side fixed shaft 4 a by screwengagement. A rotating vane (impeller) 9 is fitted onto the pump-sidefixed shaft 4 b via a bearing 10. The bearing 10 is constructed byattaching ceramic rings 12, which receive the load in the thrustdirection, at both ends in the axial direction of a cylindrical carbonring 11 that is impregnated with metal. The carbon ring 11 is bonded tothe impeller 9. The impeller 9 slidably rotates around the pump-sidefixed shaft 4 b via the carbon ring 11. The impeller 9 is provided witha coupling magnet 13 that faces the magnet 5. The magnets 5, 13 aremagnetized with six poles, for example, and the rotor 1 and the impeller9 integrally rotate due to magnetic coupling. The impeller 9 isintegrally formed by welding an upper portion, on which radiatingprotruding ribs 9 a (see FIG. 3A) are formed, and a lower portion, inwhich the coupling magnet 13 is enclosed.

In FIG. 1, the pump chamber 8 is integrally formed by screwing togethera pump case 18 and a motor case 19 via a divider plate 20. The pumpchamber 8 is sealed by an O ring 28 provided between the pump case 18and the divider plate 20. An inlet 21 for liquid is formed at the coreof the pump case 18 and an outlet 22 for the liquid (see FIG. 3A) isprovided at the outer circumferential edge. A guide tube 23 is providedcoaxially with the pump-side fixed shaft 4 b inside the pump chamber 8.That is, the guide tube 23 is fitted into and makes sliding contact witha case inner wall surface 24 that forms the pump chamber 8 and an innerwall surface 25 of an erected wall 26 erected at the core of theimpeller 9. The ends of the guide tube 23 in the axial direction arerestrained by the pump case 18 and the impeller 9. The impeller 9slidably rotates in contact with an outer circumferential surface of theguide tube 23.

In FIG. 3B, a sliding contact surface of the guide tube 23 is producedby having an outer circumferential surface of the guide tube 23 swelloutward. More specifically, a spherical surface portion 23 a whosecenter O lies on the axis M of the pump-side fixed shaft 4 b is formedat two positions. In FIG. 4, in the present embodiment, since thedistance from the axis M to the case inner wall surface 24 and thedistance from the axis M to the inner wall surface 25 of the erectedwall provided at the core of the impeller 9 are both r, sphericalsurface portions 23 a with the radius r are formed at two positions onthe sliding contact surface. The respective radii r may differ in a casewhere the distance from the axis M to the case inner wall surface 24 andthe distance from the axis M to the inner wall surface 25 of the erectedwall of the impeller 9 differ. In FIG. 4, even if the pump-side fixedshaft 4 b is inclined with respect to the axis M at the axis M′ and theimpeller 9 is inclined in the same way, even though the contactpositions between one spherical surface portion 23 a and the case innerwall surface 24 and between the other spherical surface portion 23 a andthe inner wall surface 25 of the erected wall of the impeller 9 willchange, there will be no change in the sliding contact between the guidetube 23 and the pump case 18 and impeller 9. This means that the gap Sbetween the impeller 9 and the pump case 18 can be effectively blockedby the guide tube 23.

When the motor is started, the impeller 9 that is magnetically coupledto the rotor 1 rotates, liquid is drawn from the inlet 21 in the axialdirection (the direction of the arrow P) into the pump chamber 8, andthe liquid is guided by rotation of the impeller 9 from the core of thepump case 18 in the direction of the arrow Q toward the outer peripheryand is expelled from the outlet 22 that is provided in the outerperiphery of the pump case 18 as shown in FIG. 3A. A pressure differenceis produced inside the pump chamber 8 due to the centrifugal forcecaused by the rotation of the impeller 9, and although liquid in theouter periphery that is at a high pressure attempts to flow back via thegap S between the impeller 9 and the pump case 18 in the direction ofthe arrow R toward the core that is at low pressure, such flow iseffectively blocked by the guide tube 23. Accordingly, since there areno vigorous collisions between liquid that has flowed back toward thecore and the liquid drawn in from the inlet 21, an improvement of 20 to30% or more in pump efficiency can be expected.

Note that although there is a slight backflow of the liquid due to thesliding movement of the spherical surface portions 23 a of the guidetube 23 and the case inner wall surface 24 and the inner wall surface 25of the erected wall, this has very little effect on pump operation.Also, as shown in FIG. 4, since the guide tube 23 will become inclinedin keeping with any inclination of the pump-side fixed shaft 4 b andwill maintain the sliding contact, there will be no vigorous collisionsbetween liquid that has flowed back through the gap S and the liquiddrawn in from the inlet 21.

Next, one example of an assembling process for the above pump drivingapparatus will be described with reference to FIG. 3.

Since there are no particular limitations on the type of motor, thedetails of the assembling of the motor are omitted here, and thefollowing description will focus on the assembling of the pump.

The magnet case 6 into which the coupling magnet 5 has been fitted isfitted via the bearing 7 onto the motor-side fixed shaft 4 a of themotor M (see FIG. 1). The divider plate 20 that acts as a divider forthe pump chamber is screwed to an upper surface of the motor case 19.The ceramic rings 12 are fitted at both ends of the carbon ring 11 onthe pump-side fixed shaft 4 b. The carbon ring 11 is fixed by bonding tothe shaft hole of the impeller 9.

The impeller 9 is fitted via the carbon ring 11 onto the pump-side fixedshaft 4 b that is provided so as to protrude on the pump side, and thecoupling magnet 13 is magnetically coupled to the magnet 5 of the rotor.The erected wall 26 is provided at the core of the impeller 9 and thelower end of the guide tube 23 is fitted into the inner wall surface 25of this erected wall so that sliding contact is achieved between onespherical surface portion 23 a and the inner wall surface 25. Inaddition, the pump case 18 is placed on the motor case 19 and fixed byscrews 27. When doing so, the upper end of the guide tube 23 is fittedinto the case inner wall surface 24 at the core of the pump case 18 sothat sliding contact is achieved between the case inner wall surface 24and the guide tube 23 a (see FIG. 1 and FIG. 4).

According to the pump driving apparatus described above, when liquid isdrawn in the axial direction into the pump chamber 8 and driven in thecircumferential direction by rotation of the impeller 9, due to thepressure difference inside the pump chamber 8, high-pressure liquid thatflows back via the gap S between the impeller 9 and the pump case 18 iseffectively blocked by the guide tube 23, which makes it possible toprevent collisions with low pressure liquid drawn in at the core andthereby improve the pump efficiency. Also, since it is possible toreduce the gap S between the impeller 9 and the pump case 18, it ispossible to reduce redundant capacity of the pump chamber 8 and make thepump chamber more compact.

Next, other examples of sliding contact between the guide tube 23 andthe pump case 18 and impeller 9 will be described with reference to FIG.5A to FIG. 5C.

In FIG. 5A, an erected wall 29 and the erected wall 26, which areerected in the axial direction inside the pump chamber, are respectivelyformed on the pump case 18 and the impeller 9. Spherical surfaceportions 29 a, 26 a which are produced by having an outercircumferential surface swell outward and whose center O lies on theaxis M of the fixed shaft are respectively formed on the erected walls29, 26. These erected walls 29, 26 are fitted into a cylindrical hole ofthe guide tube 23 and make sliding contact with the guide tube 23.

In FIG. 5B, an erected wall 29 and the erected wall 26, which areerected in the axial direction inside the pump chamber, are respectivelyformed on the pump case 18 and the impeller 9. The guide tube 23 isformed with a large diameter portion 30 and a small diameter portion 31.A spherical surface portion 29 a which is produced by having an outercircumferential surface swell outward and whose center O lies on theaxis M of the fixed shaft is formed on the erected wall 29. A sphericalsurface portion 31 a which is produced by having an outercircumferential surface swell outward and whose center O lies on theaxis M of the fixed shaft is also formed on the erected wall 31. At oneend in the axial direction, the erected wall 29 is fitted into thecylindrical hole of the guide tube 23 so that the spherical surfaceportion 29 a makes sliding contact. At the other end in the axialdirection, the small diameter portion 31 is fitted into the erected wall26 so that the spherical surface portion 31 a makes sliding contact.

Note that it is also possible to reverse the up-down positions of thelarge diameter portion 30 and the small diameter portion 31 of the guidetube 23 in FIG. 5B and to form a spherical surface portion, which isproduced by having an outer circumferential surface swell outward andwhose center O lies on the axis M of the fixed shaft, on the erectedwall 26 of the impeller 9 instead of on the pump case 18.

In FIG. 5C, an erected wall 29 and the erected wall 26, which areerected in the axial direction inside the pump chamber, are respectivelyformed on the pump case 18 and the impeller 9. Protruding surfaceportions (such as curved surface portions or spherical surface portions)29 b, 26 b are formed on the inner wall surfaces of the erected wall 29and the erected wall 26. Although the protruding surface portions 29 b,26 b are not necessarily limited to spherical surface portions, suchportions need to contact the outer circumferential surface of the guidetube 23 at the top and the bottom. The guide tube 23 is fitted into theerected walls 29, 26 of the pump case 18 and the impeller 9 at both endsin the axial direction so as to make sliding contact with the protrudingsurface portions 29 b, 26 b. Note that although various examples ofsliding contact have been described earlier, it is possible to producevarious types of sliding surfaces by interchanging the spherical surfaceportions or protruding surface portions formed on the sliding surfaces.

1. A pump driving apparatus that draws in a liquid in an axial directioninto a pump chamber and expels the liquid in the circumferentialdirection using an impeller that is magnetically coupled to a rotor of amotor and rotates about a fixed shaft, the pump driving apparatuscomprising a guide tube that is provided inside the pump chamber so asto be coaxial with the fixed shaft, wherein ends of the guide tube inthe axial direction are fitted to and make sliding contact with a casewall surface that forms the pump chamber and a core-side wall surface ofthe impeller enclosed inside the pump chamber.
 2. A pump drivingapparatus according to claim 1, wherein surfaces of the guide tube thatmake sliding contact are spherical surface portions which are producedby having an outer circumferential surface of the guide tube swelloutward and whose respective centers lie on an axis of the fixed shaft,and both ends of the guide tube in the axial direction are fitted intoand make sliding contact with the pump case and an uprising wall surfaceof the impeller.
 3. A pump driving apparatus according to claim 1,wherein surfaces of the pump case and the impeller that make slidingcontact are spherical surface portions that are each produced by havingan outer circumferential surface of an erected wall, which is erected inthe axial direction inside the pump chamber, swell outward and whosecenters lie on an axis of the fixed shaft, and are fitted into a tubehole of the guide tube so as to make the sliding contact.
 4. A pumpdriving apparatus according to claim 1, wherein at one end in the axialdirection, a spherical surface portion that is produced by having anouter circumferential surface of an erected wall, which is erected inthe axial direction inside the pump chamber, swell outward and whosecenter lies on an axis of the fixed shaft is formed on one of the pumpcase and the impeller and the spherical surface portion is fitted into atube hole of the guide tube so as to make sliding contact, and atanother end in the axial direction, a spherical surface portion that isproduced by having an outer circumferential surface of the guide tubeswell outward and whose center lies on the axis of the fixed shaft isformed on the guide tube and the spherical surface portion is fittedinto an erected wall of one of the pump case and the impeller.